Many types of dental cements have become available and used in a wide range of applications. Representative examples of dental cements which are mainly used at present include zinc phosphate cements which utilize a reaction between zinc oxide and phosphoric acid; polycarboxylate cements which utilize a reaction between zinc oxide and a polycarboxylic acid; zinc oxide-eugenol cements which utilize a reaction between zinc oxide and eugenol; glass ionomer cements which utilize a reaction between a fluoroaluminosilicate glass powder and a polycarboxylic acid; and resin cements which utilize a polymerization of an acrylic monomer.
Each of these dental cements has merits and demerits. For instance, the zinc phosphate cements have no adhesive properties to a tooth structure and possess irritation of phosphoric acid at the initial stage of the curing; the polycarboxylate cements are low in the final strength of a cured product; and since the zinc oxide-eugenol cements are low in the strength and inferior in the intraoral durability, their use is limited to the temporary sealing, and the eugenol per se possess irritation. Also, though the resin cements have merits such as superior adhesive properties and high mechanical strength unlike other dental cements, they involve such defects that their operation is complicated and that their bioaffinity is questionable.
On the other hand, the glass ionomer cements are quite good in the affinity to living bodies and have good dentinal adhesive properties. Moreover, they are expected to have a caries preventing effect by the fluorine contained in the glass. While utilizing these many characteristic features, the glass ionomer cements are used in a wide range of applications such as filling and restoration of caries cavity; cementing of, for example, a crown, an inlay, a bridge, or an orthodontic band; lining of cavity; core construction; and pit and fissure sealing.
In addition, there are presently developed resin-reinforced glass ionomer cements in which the brittleness of a matrix by water at the time of the initial curing, which has hitherto been considered to be a disadvantage, is prevented, and the physical properties such as mechanical strengths, e.g., bending strength, and adhesive strength to a tooth structure are improved, and which have superior adhesive properties to dental metals, resins, porcelains, etc., upon addition of a polymerizable resin component to the liquid component of the glass ionomer cement.
As described above, the glass ionomer cements have various characteristic features. However, the conventional dental glass ionomer cements are constructed from a powder component and a liquid component and involve a drawback such that the operations such as weigh and mixing are complicated. The operation of mixing of a powder component with a liquid component is usually carried out on an exclusive mixing paper by using a spatula. However, at this time, since the powder component and the liquid component are not compatible with each other, the collected powder component is divided into two parts or four parts, which are then successively mixing with the liquid component. That is, the mixing operation is required such that the powder component and the liquid component are mixed with each other uniformly as far as possible. In addition, the mixing operation must be carried out within a short period of time, and in order to fully exhibit the characteristics of the materials to be used, a remarkably skilled technique is needed.